Joke’s on you

Stop it! You’re killing me!: Knowledge-economy titans Google and Twitter indulged themselves on April Fool’s Day with announcements of mock new products and makeovers, such as Google’s Smell-O-Vision-inspired “Nose Beta.”

Meanwhile, YouTube got into the act by announcing it was shutting down — making the days of millions for a second or two before they realized it was just a gag.

Hide the mouthwash, too: Lindsay Lohan is scheduled to sit down with David Letterman for the first time in six years on April 9.

In preparation for the troubled actress’ visit, Letterman’s staff reportedly was busy making sure the green room will be drier than Mitt Romney’s New Year’s Eve party.

Sullen test subjects: Neuroscientists at the University of California-Davis have cracked one of humankind’s greatest mysteries: just what goes on inside the brains of teenagers.

The researchers’ major breakthrough took place after they reprogrammed their brain-wave machines to spell out the words “Whatever! Just leave me alone!”